Post on 22-Dec-2015
Observations from Observations from Router-level TracesRouter-level Traces
Lisa AminiIBM T. J. Watson Research Center
Joint with Henning Schulzrinne, Aurel LazarColumbia University
ContextContext Near-term issues facing service providers
for Web-facing applications Mirrored servers
where to place servers? which network access providers? how many connection points? how many servers to deploy? where to direct clients?
End-to-end routing behavior/delay vs. connectivity
AS level focus
Beyond ConnectivityBeyond Connectivity Inter-domain (AS) routing tables
Aggregation Policy-based routing Oregon Route Server
Stub Networks
Transit Networks
A
CED
B
Autonomous Systems
TracerouteTraceroute Router-level end-to-end probing
Traceroute.org website AS lookup via Routing Arbiter Database (RADB) Round trip time (RTT) Loose source-routing Artifacts
D1 DatasetD1 Dataset 189 sites Random pairings
Forward and reverse paths Poisson arrivals Mean time between probes 10 minutes 220,551 measurements 5 days 1/3 US sites, 2/3 non-US (31 countries)
[ Zhang, Duffield, Paxson, Shenker]
Router-level Path LengthRouter-level Path Length mean=16.45, std. dev.=4.39
Num
ber
of R
oute
s
0 5 10 15 20 25 300
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
Routes with US endpoints
Routes with European endpoints
All routes
Router Hops
AS Path LengthAS Path Length
0 5 10 15 20 25 300
0.5
1
1.5
2
2.5
3
3.5x 10
4
All routesUS only routesEuropean only routes
AS Hops
Num
ber
of R
oute
s mean=6.47, std. dev.=2.33
AS Degree FrequencyAS Degree Frequency Faloutsos3 -0.97 (or higher) correlation coefficient98% of nodes represented
AS degree Frequency
100
101
102
103
100
101
102
103
All Routes
Routes with US endpoints
Rank
0.97 correlation coefficient required discarding 31% of nodes
AS FrequencyAS Frequency
AS frequency
100
101
102
103
100
101
102
103
104
All Routes
Routes with US endpoints
Rank
0.97 correlation coefficient required discarding 10% of nodes
Response Time PredictionResponse Time Prediction Does path length predict delay?
Probe Round Trip Time
Router Hops
mean RTT=263msCorrelation coefficient= 0.31
Correlation coefficient =0.27
AS Hops
AS PropertiesAS Properties Can we predict delay based on AS
path properties? Ranked each AS according to:
AS edge degree AS frequency
Calculated mean RTT per path length Grouped by top 5, 6-10, 10-20 AS’s
Influence of Path PropertiesInfluence of Path PropertiesHigh edge degree AS?
Number of Router Hops / Path
Average RTT
0 5 10 15 20 25 300
100
200
300
400
500
600Top 5 AS'sTop 10 AS'sTop 20 AS's
High Frequency AS?High Frequency AS?
0 5 10 15 20 25 300
100
200
300
400
500
600Top 5 AS'sTop 10 AS'sTop 20 AS'sAll AS's
Number of Router Hops / Path
Average RTT
High Edge Degree AS?High Edge Degree AS?High edge degree AS in 2 AS hops?
Number of Router Hops / Path
Average RTT
0 5 10 15 20 25 300
100
200
300
400
500
600Top 5 AS'sTop 10 AS'sTop 20 AS's
Backbone AS?Backbone AS?
Number of Router Hops / Path
Average RTT
0 5 10 15 20 25 300
100
200
300
400
500
600AS's ranked 1-5AS's ranked 6-10AS's ranked 10-20All routes
[http://ratings.metrix.net 7/2001]
Backbone AS in 2 AS hops?Backbone AS in 2 AS hops?
Number of Router Hops / Path
Average RTT
0 5 10 15 20 25 300
100
200
300
400
500
600AS's ranked 1-5AS's ranked 6-10AS's ranked 10-20Remaining paths
AS Affinity?AS Affinity?
Number of Router Hops / Path
Average RTT
0 5 10 15 20 25 300
100
200
300
400
500
60040% in an AS50% in an AS60% in an ASAll
Route AsymmetryRoute Asymmetry Paxson, 1995 Path(A,B) Path(B,A) Issues
Ping triangulation Congestion Avoidance Internet mapping
A B
AS Hop DifferencesAS Hop Differences
Number of AS hop differences
Number of Routes
0 2 4 6 8 10 12 1410
0
101
102
103
104
105
All RoutesUS Endpoint RoutesEU endpoint Routes
11755 paired, unique routes
57% routes were AS-path asymmetric
Compare with 30% based on 1995 data
74% asymmetric from first AS hop
BGP AS PathBGP AS Path
Can we predict forward and reverse end-to-end metrics from BGP AS_PATH?
Looking Glass Probing 92 Sites 8372 unique path measurements 2202 fully paired (BGP forward and
reverse, traceroute forward and reverse)
AS Hop DifferencesAS Hop Differences
Number of AS hop differences
Number of Routes
0 5 10 15 200
500
1000
1500traceroute reverseBGP forwardBGP reverse
47% of forward paths correctly predicted by reverse traceroute
49% of forward paths correctly predicted by reverse BGP AS_PATH
69% of forward paths correctly predicted by forward BGP AS_PATH
34% asymmetry between forward/reverse BGP AS_PATH
SummarySummary BGP routing tables provide complete view
from single location. Aggregation Filtering
End-to-end probing from points throughout network can provide insights beyond connectivity Limited view of connectivity Traceroute issues with noise, node
assignment BGP AS_PATH inaccurate as path predictor
Discard CriteriaDiscard Criteria• Origin traceroute server not
responding• Incomplete traceroute output• Internal use only node address (e.g.,
10.x.x.x, 172.16.x.x-172.32.x.x ranges)• Route did note terminate in target AS• Intermediate node did not respond to
ICMP echo• No matching reverse probe for same
time period